Iranian missile technicians secretly visited North Korea as part of joint development of a new rocket booster for long-range missiles or space launchers at the same time nuclear talks took place in Geneva, according to U.S. officials.

Several groups of technicians from the Shahid Hemmat Industrial Group (SHIG), a unit in charge of building Iran's liquid-fueled missiles, traveled to Pyongyang during the past several month, including as recently as late October, to work on the new, 80-ton rocket booster being developed by the North Koreans, according to officials familiar with intelligence reports.

The booster is believed by U.S. intelligence agencies to be intended for a new long-range missile or space launch vehicle that could be used to carry nuclear warheads, and could be exported to Iran in the future.

Recent U.S. intelligence assessments have said that both North Korea and Iran are expected to have missiles capable of hitting the United States with a nuclear warhead in the next two years.

The Iranian cooperation reveals that the nuclear framework agreement concluded Sunday in Geneva has not slowed Tehran's drive for missiles that can deliver a nuclear warhead to intercontinental range.